This invention relates to multi-layer boards for interconnecting electronic components, and has particular relation to the fabrication of such boards without any drilling thereof.
When computers were first developed, insulated wires ran from the appropriate electrode of each component to the appropriate electrode(s) of the appropriate other component(s). This was bulky, slow, and expensive, but it had the adventage that wires could cross over one another without passing electricity from either wire to the other.
When printed circuit boards came into use, the wire could be screened or etched into the board, compactly, quickly, and cheaply. However, wires which crossed each other would pass electricity to each other, unless a layer of insulation was laid down on top of the lower wire before the upper wire was screened or etched on. This was slow and expensive.
Thus was born the multi-layer board (MLB). A plurality of thin boards are screened or etched with a variety of wires. The thin boards are then aligned, and are glued or otherwise bonded together into a thick multi-layer board (MLB). If a wire on any thin board (layer) needs to connect with a wire on any other layer (even an adjoining layer), a hole is drilled through the entire MLB and the hole is filled with a conductor. (Of course, the wires on all the other layers have to avoid where this hole is going to be.) Electronic components can then be attached to the wires on the top layer.
The need for the wires of all other layers to avoid the location where two layers are to be connected wastes a lot of space on these other layers. Moreover, each MLB has to be separately drilled.